This invention relates to central station alarm systems, and more particularly to local control apparatus which monitors a plurality of alarm sensors and transmits selected alarm signals to a central station.
The trend in central station alarm systems is toward the use of more powerful and versatile local control units. The local control unit in such systems is typically located on the subscriber's premises and is connected to various alarm sensors (e.g., smoke detectors, heat sensors, motion sensors, entry detectors on doors and windows, water flow detectors, etc.) distributed throughout the protected premises. The local control unit monitors signals from the alarm sensors and transmits appropriate alarm signals to a remotely located central station. Operators at the central station interpret the alarm signals received at the central station and dispatch services (e.g., police, fire, or maintenance services and the like) to the subscriber's premises on the basis of the received alarm signals.
More sophisticated local control units are desirable for many reasons. A more sophisticated local control unit allows more functions to be controlled locally, thereby reducing the amount of information which must be transmitted to the central station. This increases the efficiency and lowers the operating cost of the central station because the central station operators have less information to deal with. A more sophisticated local control unit also enhances the level of protection afforded by the system because it provides better monitoring of the alarm sensors and is better able to distinguish true alarm conditions from false alarm conditions. This greatly reduces the transmission of false alarms to the central station. A more sophisticated local control unit also allows the subscriber to have much greater control over his installation without needing to interact with the central station personnel. Other advantages of advanced local control units for central station alarm systems are well known to those skilled in the art.
One of the operating difficulties in many central station alarm systems has been that subscribers frequently wish to change the time at the end of the day at which they intend to close their premises. In many systems the subscriber must telephone the central station to report a change in closing time so that the central station operators will know how to interpret signals received before and after that time. This restricts the subscriber and creates a large volume of telephone traffic for the central station. In addition, should the subscriber fail to contact the central station, operators at the central station must spend a large amount of time to contact the subscriber to obtain the new schedule or inform the subscriber that he failed to secure the premises.
It is therefore an object of this invention to provide a local control unit which eliminates the need for the subscriber to call the central station whenever he wishes to change his closing time.
Local control unit apparatus frequently includes a battery to supply power in the event that the primary alternating current ("AC") power supply fails or is interrupted. If the system has both security and fire alarm sensors, it is desirable to conserve battery power to operate the fire alarm sensors as long as possible during an AC power failure.
It is therefore another object of this invention to provide a local control unit which automatically operates to cut off power to non-fire alarm sensors during a prolonged AC power failure or when remaining battery power is low in order to conserve battery power for the longest possible continued operation of the fire alarm sensors.
Local control unit apparatus also desirably includes means for allowing an authorized operator of the local control unit to silence audible security and fire alarm indications. However, the danger exists when this capability is provided that, once activated, the silencing mechanism will be inadvertently left activated too long and prevent audible indications of a new security or fire alarm indication.
It is therefore yet another object of this invention to provide a local control unit which automatically overrides the silence mechanism when any new alarm condition is detected and which automatically deactivates the silence mechanism entirely when all alarm conditions have been corrected.
Alarm systems having a plurality of distributed alarm monitoring devices typically include two or more communication circuits extending from the control circuitry. The alarm monitoring devices are distributed along these communication circuits. If a break occurs in a communication circuit, it becomes impossible to receive alarms from the alarm monitoring devices beyond the break.
It is therefore still another object of this invention to provide a distributed alarm system in which an alternate circuit can be established when needed for communication with alarm monitoring devices beyond a break in a communication circuit.